Tropical Depression EIGHT (Text)

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006
500 PM EDT TUE SEP 12 2006
SATELLITE IMAGES SHOW THAT THE DEPRESSION IS GRADUALLY BECOMING MORE
ORGANIZED WITH FAIRLY PROMINENT BANDING FEATURES OVER THE WESTERN
AND SOUTHERN PORTIONS OF THE CIRCULATION. HOWEVER THE CENTER IS
STILL RATHER BROAD AND ELONGATED...AND THE AREA OF CONVECTION TO
THE WEST OF THE CENTER IS MOVING WESTWARD AND BECOMING MORE
SEPARATED FROM THE CENTER OF THE CYCLONE. A SHIP REPORT FROM A
VESSEL WITH CALL SIGN OVZV2 OF NORTHERLY WINDS OF 36 KT AND A
PRESSURE OF 1008.7 MB SOME 180 N MI NORTHWEST OF THE ESTIMATED
CENTER OF THE TROPICAL CYCLONE. THIS WIND OBSERVATION WAS IN
CONVECTION...PROBABLY A LOCALIZED SQUALL...AND NOT REPRESENTATIVE
OF THE STRENGTH OF THE CIRCULATION. MOREOVER...A QUALITY CONTROL
CHECK OF THIS SHIP BY THE OCEAN PREDICTION CENTER INDICATED THAT
ITS WIND MEASUREMENTS WERE A FEW KNOTS TOO HIGH AND ITS PRESSURE
HAS BEEN RUNNING 1-2 MB LOW. HAVING SAID ALL THAT...THE SYSTEM IS
NEARING TROPICAL STORM STATUS AND WILL PROBABLY BE NAMED TONIGHT OR
ON WEDNESDAY. MODEST EASTERLY SHEAR CURRENTLY PREVAILS OVER THE
AREA...AND SINCE THE SEA SURFACE TEMPERATURES ARE FAIRLY WARM...
STRENGTHENING SEEMS LIKELY IN THE SHORT TERM. GLOBAL MODELS DIFFER
IN THE DETAILS OF THE EVOLUTION OF AN UPPER-LEVEL TROUGH NEAR
40-45W NORTH OF 15N...BUT IN GENERAL THEY SUGGEST THAT IT WILL
BECOME LESS INFLUENTIAL IN SEVERAL DAYS. THE SHIPS MODEL...USING
THE GFS FORECAST FIELDS AS INPUT...SHOWS WEAK SHEAR THROUGH THE
FORECAST PERIOD. I AM NOT TOTALLY CONFIDENT THAT THE UPPER-LEVEL
ENVIRONMENT WILL REMAIN SO FAVORABLE...SO THE OFFICIAL INTENSITY
FORECAST IS MORE CONSERVATIVE THAN THE SHIPS OUTPUT AND JUST
SLIGHTLY BELOW THE CONSENSUS OF THE GUIDANCE.
A SLIGHT SOUTHWARD RELOCATION OF THE CENTER HAS BEEN DONE FOR THIS
PACKAGE...CONSISTENT WITH MICROWAVE IMAGERY...AND THE FORWARD SPEED
HAS BEEN ADJUSTED TO BE A LITTLE SLOWER. CURRENT MOTION IS
ESTIMATED TO BE 270/13. DYNAMICAL GUIDANCE INDICATES AN INCREASE
IN FORWARD SPEED OVER THE NEXT COUPLE OF DAYS...SUGGESTING A
STRENGTHENING OF THE MID-LEVEL RIDGE TO THE NORTH OF THE CYCLONE.
BY DAY 3 HOWEVER...THE GUIDANCE INDICATES THAT THE SYSTEM WILL
RESPOND TO A WEAKNESS IN THE RIDGE NEAR OR JUST WEST OF 50W...AND
BEGIN TO TURN TOWARD THE RIGHT. THE LATEST GFS...U.K. MET
OFFICE...NOGAPS...AND ECMWF GLOBAL MODELS ARE IN BETTER AGREEMENT
ON THE TRACK AT DAYS 4 AND 5. THE OFFICIAL TRACK FORECAST HAS BEEN
SHIFTED SOUTHWARD FROM THE PREVIOUS ONE FOR THE FIRST COUPLE OF
DAYS BUT IS ADJUSTED A LITTLE TO THE NORTH IN THE LATTER PART OF
THE FORECAST PERIOD. THIS IS NEAR THE LEFT EDGE OF THE TRACK
GUIDANCE ENVELOPE.
FORECAST POSITIONS AND MAX WINDS
INITIAL 12/2100Z 12.0N 23.9W 30 KT
12HR VT 13/0600Z 12.0N 26.3W 40 KT
24HR VT 13/1800Z 12.3N 29.5W 45 KT
36HR VT 14/0600Z 12.6N 33.1W 50 KT
48HR VT 14/1800Z 13.3N 36.7W 60 KT
72HR VT 15/1800Z 15.5N 42.0W 70 KT
96HR VT 16/1800Z 17.5N 46.0W 85 KT
120HR VT 17/1800Z 20.0N 50.0W 95 KT
$$
FORECASTER PASCH
NNNN